Flame Emission Research Articles

Tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions.

The method of tomographic imaging using multi-simultaneous measurements (TIMes) for flame emission reconstructions is presented. Measurements of the peak natural CH* chemiluminescence in the flame and luminescence from different vaporised alkali metal salts that were seeded in a multi-annulus burner were used. An array of 29 CCD cameras around the Cambridge-Sandia burner was deployed, with 3 sets of cameras each measuring a different colour channel using bandpass optical filters. The three-dimensional instantaneous and time-averaged fields of the individual measured channels were reconstructed and superimposed for two new operating conditions, with differing cold flow Reynolds numbers. The contour of the reconstructed flame front followed the interface between the burnt side of the flame, where the alkali salt luminescence appears, and the cold gas region. The increased mixing between different reconstructed channels in the downstream direction that is promoted by the higher levels of turbulence in the larger Reynolds number case was clearly demonstrated. The TIMes method enabled combustion zones originating from different streams and the flame front to be distinguished and their overlap regions to be identified, in the entire volume.

Combustion performance of a low NOx gas turbine combustor using urea addition into liquid fuel

The present work provides an experimental investigation on the effects of the urea addition in water emulsified fuels in terms of combustion performance and emissions. Experiments have been carried out using a test rig equipped with a 300-kW Jet-A1 fueled swirling burner operating under lean conditions. Different equivalence ratios and various urea in water percent concentrations have been tested. Measurements of temperature and emissions have been performed, in combination with high-speed flame imaging in visible and ultraviolet spectral ranges.Results have shown that the use of 2.5 wt% (percent concentration by weight) water-2 wt% urea solution into Jet-A1 fuel represents a promising combustion control strategy, since it leads to the same nitrogen oxides (NOx) reduction of a leaner neat fuel flame (about 30% less than the neat fuel case), but without significant penalty on the overall combustion performance, viz. combustion temperature, thermal and combustion efficiencies and pollutant emissions. The snapshot Proper Orthogonal Decomposition (POD) of the broadband flame emission images, methylidyne radical and hydroxyl radical chemiluminescence allowed to characterize of the flame dynamics and the flame stability. Differences between the flame regimes were also investigated by the POD mode 3 eigenstructure. The reduced flame stability for the leaner operating condition was confirmed by the energy increase of the first POD modes. The more unstable flame dynamics was confirmed by the frequency distribution of the phase points in the POD phase-space of modes 1 and 2 that highlighted a significant rise of the phase angles occurrence in the range [−π/6, π/6].

Case Study upon Foliar Application of Biofertilizers Affecting Microbial Biomass and Enzyme Activity in Soil and Yield Related Properties of Maize and Wheat Grains.

Simple SummaryThe study evaluated the effects of the application of microbial inoculants (N-fixing Klebsiella planticola and Enterobacter spp.), two rates of composite mineral fertilizers, and their combination on microbial biomass carbon, dehydrogenase and proteinase activity in acid Lessivated Cambisol and yield-related properties of maize and wheat grains in a two-year trial. The results indicated that mineral fertilizers are not, in general, negative for soil microbiota when used in the context of sustainable agriculture without monoculture. It was found that the combined application of microbial inoculants and lower doses of mineral nitrogen, phosphorus, and potassium (NPK) fertilizers, increased the yield of maize and wheat compared to the use of only NPK fertilizers in our case study. The highest values of the examined parameters of soil fertility were determined in the period with better precipitation distribution during the vegetation period of the studied year due to the optimal values of soil moisture and air temperature. Concluding, the authors point out the task of science to offer the producer a solution for conducting intensive agricultural production, which must be economically and ecologically safer.This study evaluated the effects of the application of microbial inoculants (N-fixing Klebsiella planticola and Enterobacter spp.), two rates of composite mineral fertilizers, and their combination on microbial biomass carbon (MBC), dehydrogenase (DHA), and proteinase activity (PTA) in Lessivated Cambisol and yield-related properties of maize and wheat grains in a two-year trial. Unfertilized soil was used as a control variant. MBC was measured using the chloroform fumigation-extraction method, DHA was determined spectrophotometrically by measuring the intensity of the formed red-colored triphenyl formazan, while PTA was determined using a titration method by measuring the degree of gelatine decomposition. In grain samples, P was determined spectrophotometrically, K—by flame emission photometry, N—on an elemental carbon/nitrogen/sulfur (CNS) analyzer, and crude proteins—by calculation of N content. Measuring both crops’ yield was carried out at the end of the vegetation. The results indicated that mineral fertilizers are not, in general, negative for soil microbiota when used in the context of sustainable agriculture without monoculture. There is a significant increase in the values of soil MBC, DHA, and PTA in the variants with combined application of bacterial inoculants and lower rates of mineral fertilizers. The highest values of these parameters were determined in the period with a better distribution of precipitation during the vegetation period of the year. The mentioned combination also resulted in a higher grain yield of maize and wheat comparing to the application of lower rates of the NPK nutrients solely. The combined application of high rates of mineral fertilizers and bacterial inoculants resulted in significantly increased N, P, K, and protein content in the grains of crops, and the same applied to yield. Concluding, studied bacterial inoculants can be used to specify the replacement of nitrogen fertilizers, stimulating the microbial biomass and enzyme activity in the soil, helping to ensure that the supply of nutrients contributing to an optimized yield of crops is maintained.

Femtosecond laser activation and sensing of hydroxyl for velocimetry in reacting flows.

A molecular tagging method for velocity measurements in reacting environments such as propulsion devices and high-temperature combustion-assisted wind tunnels is described. The method employs a femtosecond (write) laser to photodissociate H2O, a common combustion product, into a locally high concentration of OH radicals. These radicals are tracked by planar laser-induced fluorescence (PLIF) from the A2Σ-X2Π (1-0) vibrational band excited by a time-delayed 284 nm (read) laser sheet. As a variant of hydroxyl tagging velocimetry, the source laser can also be used to dissociate nitrogen for femtosecond laser electronic excitation tagging velocimetry to mark the time-zero location of the write laser for velocimetry in non-reacting regions using the same imaging system without OH PLIF. The OH tracer lifetime is studied in a hydrogen-air Hencken burner operating at Φ=0.5-1.8 to evaluate the tracking capability for velocimetry over a range of conditions. Effects of changing read laser wavelength, excitation energy, and influence of background flame emission are also studied. The data processing methodology and results are described for tracking displacements with 9-25 µm uncertainty in a hydrogen diffusion flame. This method presents several advantages in operational convenience and availability of laser sources, and it provides an avenue for improvements in the repetition rate, precision, and applicability over previously demonstrated hydroxyl tagging schemes.

GC-MS Analysis, Metal Analysis and Antimicrobial Investigation of Sterculia diversifolia

Plants of Sterculia genus contain various types of bioactive compounds which bears therapeutic potential. The current research was planned to perform gas chromatography-mass spectrometry (GC-MS) analysis and metal analysis, and to test the antimicrobial activity of various extracted samples of Sterculia diversifolia G. Don specie. Screening of S. diversifolia for chemical constituents was carried out using various qualitative procedures, which confirmed the existence of a number of bioactive compounds. Gas chromatography followed by GC-MS is a significant analytical tool for the assessment of composition of fixed oils or oily fractions. Atomic absorption spectrophotometer was used for the determination of micronutrients, while atomic emission flame photometer for the analysis of macronutrients. The antibacterial and antifungal activities were investigated by well diffusion and tube dilution techniques respectively. The n-hexane fractions of both the stem bark and leaves of S. diversifolia were analyzed with the help of GC-MS, resulting in the identification of 32 and 62 compounds, respectively. Various micronutrients and macronutrients shown reasonable quantities in stem bark and leaves extracts. The n-hexane and dichloromethane fractions of S. diversifolia stem bark, leaves and seeds showed mild to moderate range of antibacterial activity against Staphylococcus aureus and no antifungal activity against any fungal strain. Our findings support the use of S. diversifolia in traditional medicine.

Microwave-assisted modulation of light emission intensity in alkali-pyrotechnic plumes

Creating next-generation pyrotechnic emitters capable of dynamically controllable light output requires a paradigm shift away from emission control via formulation. This work demonstrates the ability to modulate light emission intensity of a pyrotechnic flame with 2.46 GHz microwave energy within a multimodal cavity. Stoichiometric mixtures of three pyrotechnic systems are investigated: magnesium fuel with oxidizers of NaNO3, KNO3, or CsNO3. Using time-resolved visible and infrared emission spectroscopy and high-speed color videography, microwave illumination of flames is found to produce enhanced atomic photo emission from the alkali species. Emission increases of up to ~120% are demonstrated, which are predominantly in the visible and near-infrared wavelengths and have little effect on flame emission chromaticity. At near- and mid-IR wavelengths, gray body continuum enhancement is observed with moderate enhanced emission from CO2 and H2O bands. Sustained light emission from microwave illumination of combustion products long after pyrotechnic extinguishment was also demonstrated. A simplified model of microwave-enhanced visible and near-IR emission is presented and shown to be consistent with the observed trend of elevated emission enhancement for lower wavelength alkali transitions. Sensitivity analysis is performed which suggests a lower equilibrium population of electronically excited alkali atoms is primarily responsible for maximizing the degree of light emission enhancement of applied microwave fields, especially in extinguished low-temperature pyrotechnic plumes. These findings suggest microwave illumination of alkali-containing pyrotechnic flames may be a useful strategy to achieve dynamic control of light emission intensity.

Numerical research on combustion and emissions behaviors of a medium compression ratio direct-injection twin-spark plug synchronous ignition methanol engine under steady-state lean-burn conditions

Twin-spark plug synchronous ignition is an effective means of improving the stability of combustion and extending the lean-burn limit of the spark ignition engine. In this study, the distribution of mixture concentration, combustion, and emissions-related behaviors of a direct-injection twin-spark plug synchronous ignition methanol engine are numerically investigated to assess its lean-burn performance and solve for stable combustion under a medium compression ratio. The simulation results shows that the timing of the injection and ignition, and the distribution of flow velocity at ignition determine the distribution of the mixture concentration in the cylinder, which in turn affects the density of the flame surface and emissions. The delay ignition timing, the unburned methanol emissions increase significantly, while the nitrogen oxides emissions decrease rapidly. Optimal injection timing of 110°crank angle before top dead center and ignition timing of 21°crank angle before top dead center could obtain the best compromise of a medium compression ratio direct-injection twin-spark plug synchronous ignition methanol engine under steady-state lean-burn conditions. Thus, twin-spark plug synchronous ignition can ensure stable combustion and yield good performance with a medium compression ratio under lean-burn conditions.

Flame stability and emissions characteristics of liquid ammonia spray co-fired with methane in a single stage swirl combustor

Direct combustion of liquid ammonia spray can reduce the cost and start-up time required for gas turbines fuelled with otherwise gaseous ammonia. This article reports the first successful study on liquid ammonia spray combustion in a novel swirl combustor with preheated air at 500 K. Particle Image Velocimetry (PIV) was employed to measure the non-reacting air flow field in the combustor while the liquid ammonia spray was visualized by Mie scattering techniques. Emissions from the flame were analysed using a Fourier Transform Infrared spectrometer. The present combustor encouraged a large central reverse flow, counter flowing with the spray. Hence, the preheated air enhanced the dispersion and evaporation of the liquid droplets, and thus promoted shorter spray heights. Stable combustion of liquid ammonia spray alone was achieved, while co-combustion with methane enhanced the combustion of the spray and reduced the flame height. For 70% ammonia fraction in the fuel by lower heating value, the flame was stable for global equivalence ratios, ϕ, between 0.66 and 1.37. The stability range narrowed as ammonia fraction and swirler mean inlet velocity increased. Emission analysis from the co-combustion shows that an optimum low emission ϕ exists at 1.06, thus rich-lean combustion can be employed in two-stage combustors to further control emissions from the spray flame when the primary zone ϕ is slightly rich. Numerical analysis indicates that the large latent heat of vaporization of liquid ammonia may contribute to a shift of the low emission ϕ towards leaner values.

Optical diagnostics on the effects of reverse reactivity stratification on the flame development in dual-fuel combustion

The effects of reverse reactivity stratification, i.e., port-injection (PI) of n-heptane with direct-injection (DI) of iso-octane and PI of iso-octane with DI of n-heptane, on combustion characteristics and flame development were investigated. The volume fractions of port-injected fuel were 30%, 70% and 90%. The DI timings were −25°, −15° and −5° CA ATDC. The optical diagnostic methods of high-speed imaging and flame emission spectra were adopted. Results show when n-heptane is port injected and iso-octane is direct injected, the PI volume fraction plays more important role in controlling combustion phasing, while the DI timing is the dominant factor on flame development structure that can be classified into four classes. When iso-octane is port injected and n-heptane is direct injected, the DI timing dominates the combustion phasing. Flame kernels merge to form larger flame area with reactivity stratification introduction compared with the condition that nearly only one initial flame kernel forms in each downstream spray without reactivity stratification introduction. The initial mean flame speed is around 80 m/s with reactivity stratification introduction, which is nearly twice faster than that without reactivity stratification introduction. Finally, when comparing conditions of reverse reactivity stratification, it provides guidance for dual-fuel combustion engines that the overall reactivity cannot be regarded as the solely important parameter to optimize combustion phasing and other combustion characteristics. At some extent, the effects of overall reactivity on combustion characteristics are lower than the effects of volume fraction, equivalence ratio, injection order or start of injection (SOI) timing of high reactivity fuel.

Exploring Emission and Absorption Spectroscopy in the First-Year General Chemistry Laboratory

In the first-year general chemistry laboratory course, instrumental data collection involving sample quantification has often been limited to absorption spectroscopy due to the inaccessibility of emission techniques suitable for large enrollments and novice users. In this laboratory experiment, students explore the complementary techniques of emission and absorption spectroscopy, in which sample quantification respectively occurs via the measurement of light emitted or absorbed by the sample. Calibration curves are constructed for both techniques. Eschewing atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES), instrumentation not typically available for large general chemistry courses, quantitative data is instead collected using a series of carefully implemented flame tests. Students perform flame tests on alkali, alkaline earth, and transition metal compounds using the emitted light to gain a thorough understanding of emission spectroscopy. In Week 1, students are introduced to emission spectroscopy through the identification of unknown components in air, lamps, and contaminated soil samples. In Week 2, students carry out quantitative emission and absorption characterization of Na and Cu solutions, comparing the two techniques through experimental observations and analyzed results. Calibration curves with high linear regressions (r2 > 0.992) are prepared and used to determine the concentrations of provided reference samples, with averaged student data resulting in reasonably low percent errors (<12% for Na emission, <11% for Cu emission, and <2% for Cu absorption) when compared to the known concentrations. Students then compare experimental flame emission results to provided ICP data to gain experience with a sensitive, quantitative emission technique.

Heat transfer characteristics of flame jet impingement with methane air reaction environment

Abstract The high heat transfer rate achieved in flame impingement technique makes it suitable for various industrial heating operations which demands rapid heating. The geometric parameters of flame jet impingement has significant effect on heat transfer rate. One of these parameters is h/d (h is distance between flame emission nozzle and base plate while d is diameter of nozzle) which has significant effect on heat transfer rate. The current research investigates the effect of this geometric parameter i.e., h/d using techniques of Computational Fluid Dynamics. The CAD model of flame jet computational domain of different h/d ratio (1.2, 1.6, 2, and 2.4) is developed in Creo design software and CFD analysis is conducted using ANSYS CFX software package. Eddy dissipation model is used for combustion modelling and RNG k-epsilon model is used for turbulence. The temperature plot and heat flux plot generated from analysis predicted heat transfer rate at stagnation point.

Coupling Analysis of Chemiluminescence and Pressure Changes in CH4/Air Explosion Suppressed by NaHCO3 Powder.

This paper presents the coupling relationship between the flame emission spectrum and explosion characteristics of CH4/air mixtures with NaHCO3 powder added. Due to the test of different concentrations of suppression powder in 20 L spherical-explosion-test devices, the flame emission spectrum and explosion pressure data were collected. In this experiment, four kinds of excited radicals, including CN*, HCHO*, CO*, and OH*, have a higher probability of being detected, and the changes of their existence duration and spectral intensity show strong regularity. Results reveal that for suppressant concentration in the range of 0–50 mg/L, together with the improvement of a suppression effect, the existence duration and spectral intensity of CN*, CO*, and OH* decrease, which is opposite to that of HCHO*. Besides, the spectral intensity of OH* and CO* shows a good linear relationship with the change of the maximum explosion pressure. Controlling the content of CN*, CO*, OH*, and HCHO* is of great significance in suppressing the explosion.

An in-situ method for time-resolved sodium release behaviour during coal combustion and its application in industrial coal-fired boilers

To mitigate the slagging, fouling and high-temperature corrosion problems caused by alkali metals during coal combustion process, measurement of time-resolved alkali metals release is very important. The paper proposed an in-situ approach for measuring sodium (Na) release in coal combustion by Flame Emission Spectroscopy (FES). Through the analysis of spontaneous emission spectra and a calibration procedure, the concentration of gas phase Na, temperature and thermal radiation can be obtained. Firstly, experimental measurement of Zhundong coal particles burning in a flat flame burner was done. Two kinds of Zhundong coal with similar proximate and ultimate analyses, but different ash composition were used. The Na-release history measured by FES was compared with that by LIBS. Results showed that the Na-release at the devolatilization, char, and ash stages can be distinguished by FES. The higher Si/Al content in ash can suppress the Na-release at the ash stage. Moreover, FES method was extended to the measurement of Na-release in four industrial boiler furnaces of two Zhundong coal-fired power plants. Results showed the Na-release measured by FES can reflect the change of fuel and load, and both temperature and thermal radiation play key roles in Na-release in coal combustion.

Study on the effect of 2-butoxyethanol as an additive on the combustion flame, performance and emission characteristics of a spark ignition engine

This research work endeavours to study the effect of 2-butoxyethanol blended gasoline on the engine in-cylinder spatial flame propagation, performance, and emission characteristics of a twin-cylinder spark ignition engine at a constant speed of 2400 rpm. The four blends were prepared by adding 1%, 1.5%, 2%, and 2.5% 2-butoxyethanol by volume proportion to the sole gasoline. The visual characteristics of the spatial combustion flame propagation were studied by flame visualization technique using engine endoscope. The captured flame propagation images were analyzed by the combustion diagnostic tool and digital image processing method to compute the flame speed. The results show that the percentage increase in flame speed for 2BE10, 2BE15, 2BE20, and 2BE25 blends is 0.046%, 0.2%, 0.8%, and 1.4% respectively as compared with gasoline. The peak in-cylinder pressure and heat release rate of 2BE25 (97.5% gasoline + 2.5% butoxyethanol) fuel blend is higher by 1.9 bar and 5.06 kJ/m3deg when compared to the sole gasoline whose values are 31.35 bar and 74.322 kJ/m3deg. All the butoxyethanol blends showed a slight improvement in brake thermal efficiency. At full load condition, the CO and HC emissions of 2BE25 blend are decreased by about 15.6% and 9% respectively, whereas NOx emissions of 2BE25 are increased by 10% when compared to that of sole gasoline.

Effect of different syngas compositions on the combustion characteristics and emission of a model combustor

There is a growing need to design fuel flexible combustors. This require understanding of the combustion and emission characteristics of the combustors under varying fuel compositions. In the present study, the combustion characteristics and emission of methane and syngas flames were investigated numerically in a swirl stabilized combustor. The numerical model was developed using ANSYS-fluent software and validated using experimental values of temperature, CO2 and NOx emissions. A two-step chemical mechanism was used to model methane-air combustion. Results of the numerical validation showed similar trend between the experimental and predicted temperature along the combustor axis with about 5 % over prediction of the temperature. Syngas-air combustion was thereafter modeled using a 21 step chemical mechanism. Syngas compositions studied were: syngas A (67% CO: 33% H2), syngas B (50% CO: 50% H2) and syngas C (33% CO: 67% H2). Results showed that for pure methane, a V-shaped flame was observed with the flame attached to the fuel nozzle, while a lifted flame was observed for case of syngas A composition. CO gas with higher ignition temperature and flammability as compared to H2 gas is the dominant gas in syngas A fuel composition. Jet flames were observed for syngas B and syngas C. Carbon monoxide is a slow burning gas. Therefore syngas with low CO content has a low tendency of emission of CO from the combustor. This suggests that syngas with high CO content such syngas A may require more residence time to completely combust the CO gas. The NOx emission was observed to have the same trend as that of the combustor maximum temperature. Syngas C flame had the highest NOx emission, while, syngas A flame had no NOx emission. This is due to low combustor temperature observed in the case of syngas A flame.&#x0D; Keywords: Syngas, ANSYS-FLUENT, Swirl-stabilized combustor, NOx emission, Chemical Mechanism

NO and OH* emission characteristics of very-lean to stoichiometric ammonia–hydrogen–air swirl flames

One of the main concerns regarding ammonia combustion is its tendency to yield high nitric oxide (NO) emissions. Burning ammonia under slightly rich conditions reduces the NO mole fraction to a low level, but the penalties are poor combustion efficiency and unburnt ammonia. As an alternative solution, this paper reports the experimental investigation of premixed swirl flames fueled with ammonia-hydrogen mixtures under very-lean to stoichiometric conditions. A gas analyzer was used to measure the NO mole fraction in the flame and post flame regions, and it was found that low NO emissions (as low as 100 ppm) in the exhaust were achieved under very lean conditions (ϕ ≈ 0.40). Low NO emission was also possible at higher equivalence ratios, e.g. ϕ = 0.65, for very large ammonia fuel fractions (XNH3 > 0.90). 1-D flame simulations were performed to elaborate on experimental findings and clarify the observations of the chemical kinetics. In addition, images of OH* chemiluminescence intensity were captured to identify the flame structure. It was found that, for some conditions, the OH* chemiluminescence intensity can be used as a proxy for the NO mole fraction. A monotonic relationship was discovered between OH* chemiluminescence intensities and NO mole fraction for a wide range of ammonia-hydrogen blends (0.40 < ϕ < 0.90 and 0.25 < XNH3 < 0.90), making it possible to use the low-cost OH* chemiluminescence technique to qualify NO emission of flames fueled with hydrogen-enriched ammonia blends.

Analytical methods assessment for exchangeable cations analysis in soil: MIP OES appraisement

ABSTRACT Soil monitoring and research often requires a comparison of laboratory data generated by diverse instruments and in different laboratories to demonstrate the reliability and accuracy of the results. The outcomes of this work highlight a performance comparison among different analytical methods for the determination of calcium (Ca), magnesium (Mg), sodium (Na), and potassium (K), in soil. Five soil samples were used for analytical methods comparison, corresponding to an argentine agricultural soil interlaboratory, and four soil samples from the Pampa region of Argentina were used for analytical application of the instrumental methods. The results obtained with flame atomic absorption and emission spectrometry (FAAS-FAES) and microwave-induced plasma optical emission spectrometry (MIP OES) were compared to those obtained by conventional analytical methods as complexometric titration and flame photometry. As there were no significant differences between classical methods with instrumental ones, FAAS-FAES and MIP OES were validated following criteria based on international guidelines. Accuracy, precision, linearity, limits of detection and quantification, sensitivity, analytical sensitivity, and working range were evaluated. The results established the satisfactory performance of FAAS-FAES and MIP OES for exchangeable cations. MIP OES is an efficient alternative to FAAS-FAES, with wide linear dynamic range, which is advantageous concerning to the concentrations in which these exchangeable cations are found in soils, avoiding sample dilutions. The most remarkable advantage of MIP OES is the low running costs as it does not use flammable and toxic gases. Due to its benefits MIP OES could be recommended as the main analytical method for exchangeable cations determination.

Spatiotemporal flame propagations, combustion and solid particle emissions from lean and stoichiometric gasoline direct injection engine operation

Increased particle number and mass emissions in gasoline direct injection (GDI) engines should require to investigate in-cylinder flame and combustion characteristics associated with primary source of particle emissions. In this work, in-cylinder spatiotemporal flame luminosity is quantitatively characterized to features combustion process and solid particle emissions from a GDI engine operating in two lean and one stoichiometric modes. Low- and high-steady state operating points were used to compare combustion strategies on flame development and emission characteristics. A fiber-optic sensor composed of eight measurement channels detected the flame front and the direction of the flame propagation in the combustion chamber. Solid particle emissions in the exhaust were measured using an engine exhaust particle sizer and a micro soot sensor. Results of the experiments showed that two lean combustion modes by injection strategies resulted in distinct combustion and flame development. Lean combustion modes generated high diffusion flame by burning stratified rich-mixture. Although the lean cases resulted in strong diffusion flames, the lean-homogeneous produced similar particle size distributions with the stoichiometric mode with high ash particles. Piston pool fires on the piston surface in the lean-stratified mode induced a large accumulation mode with high particle mass concentrations.

Predicting radiative heat fluxes from two buoyant turbulent diffusion flames from burning propane under cross wind

Experimental investigations were carried out to estimate the radiative heating that occurs downstream of wind-driven buoyant turbulent diffusion flames produced by twin square propane burners aligned parallel to the cross wind. During the experiments, the heat release rate, cross wind velocity, and burner edge spacing were changed. Considering the effect of wind on flame shapes, a new triangular prism flame model was established to predict the radiant heat flux received by downstream objects from two buoyant turbulent diffusion flames under cross wind. The flame radiations to downstream ground were measured by five radiometers, and the relevant parameters of the flame model were analyzed. The results show that the radiative heat flux decays with increasing flame spacing and intensifies with increasing wind velocity. A piecewise function for the flame drag length in various flame merging stages is established. The effect of wind velocity and flame spacing on flame emissivity is relatively limited, and flame emissivity is formulated as a function of the heat release rate. The view factor between the triangular prism flame model and external targets is calculated based on the contour integral method. Finally, prediction results between the proposed triangular prism flame model and conventional models are compared against experimental data. The results confirm that the new triangular prism flame model can better predict the thermal radiation from two interacting flames in the wind.

Experimental and theoretical research on flame emissivity and radiative heat flux from heptane pool fires

This paper presents an experimental investigation on the flame radiation characteristics of pool fire, including the flame emissivity, diameter and temperature. A series of experiments of heptane pool fires with diameters of 0.1–0.4 m were carried out. The flame height, mass loss rate, temperature distribution, flame emissivity and radiative heat flux were measured. A four regions function was used to correlate the centerline temperature rise above the pool surface with the flame height. The variations of the flame diameter against the flame height were formulated for D>0.2 m and D ≤ 0.2 m respectively. The highest flame emissivity is found at the flame base, which decreases with increasing height. Furthermore, a new model predicting the radiative heat flux based on classical solid flame model is developed taking into account the flame emissivity, diameter and temperature variations along the flame height. The comparisons between the new model and other models show that the new model can better predict the thermal radiation from heptane pool fires.